Content server: Add Next/Previous buttons to the book details page

src/pyj/book_list/book_details.pyj

@@ -11,7 +11,7 @@ from book_list.delete_book import refresh_after_delete, start_delete_book
 from book_list.globals import get_session_data
 from book_list.item_list import create_item, create_item_list
 from book_list.library_data import (
-    all_libraries, book_metadata, cover_url, current_library_id,
+    all_libraries, book_after, book_metadata, cover_url, current_library_id,
     current_virtual_library, download_url, library_data, load_status,
     set_book_metadata
 )
@@ -465,6 +465,21 @@ def render_book(container_id, book_id):
     table = E.table(class_='metadata')
     container.appendChild(md)
     md.appendChild(table)
+
+    def next_book(delta):
+        next_book_id = book_after(book_id, delta)
+        if next_book_id:
+            q = parse_url_params()
+            q.book_id = next_book_id + ''
+            show_panel('book_details', query=q)
+
+    md.appendChild(E.div(
+        style='margin-top: 1.5ex',
+        create_button(_('Previous'), 'arrow-left', next_book.bind(None, -1)),
+        '\xa0\xa0\xa0',
+        create_button(_('Next'), 'arrow-right', next_book.bind(None, 1)),
+    ))
+
     render_metadata(metadata, table, book_id)
 
 

src/pyj/book_list/library_data.pyj

@@ -106,14 +106,14 @@ def current_book_ids():
     return library_data.previous_book_ids.concat(library_data.search_result.book_ids)
 
 
-def book_after(book_id):
+def book_after(book_id, delta):
+    if not delta:
+        delta = 1
     ids = current_book_ids()
     idx = ids.indexOf(int(book_id))
     if idx > -1:
-        if idx < ids.length - 1:
-            return ids[idx + 1]
-        if idx > 0:  # wrap around
-            return ids[0]
+        new_idx = (idx + ids.length + delta) % ids.length
+        return ids[new_idx]
 
 
 def on_data_loaded(end_type, xhr, ev):